The invention relates generally to sealable valve bags and, more specifically to the valve sleeve used to fill and seal the valve bags. These shipping sacks are commonly used to contain and transport granular products, examples of which are fertilizers, animal feeds or grain.
Flexible bags such as paper shipping sacks may include a sealable valve sleeve placed in a filling valve, the filling valve is located in a corner of the flexible bag to allow introduction of material that is to be held within the bag. These shipping sacks are commonly used to contain and transport material such as granular products, examples of which are fertilizers, animal feeds or grain. The sealable sleeve provides a convenient means to fill and securely close the flexible bag to prevent the contents of the bag from leaking or sifting out of the bag once the bag has been filled. Sleeves may be constructed of a variety of materials such as paper, polyethylene tubing or a thermoplastic liner.
A typical sleeve for a paper shipping sack, such as a pasted valve type multiwall shipping sack, is made from a rectangular sheet of kraft paper that is rolled into a cylindrical shape and secured in the cylindrical shape by overlapping or abutting the opposing edges of the sheet of paper to one another and gluing to form a seam. Such a sleeve is described in commonly assigned U.S. Pat. No. 6,164,823, the disclosure of which is hereby expressly incorporated by reference. In order to seal the valve sleeve and therefore the valve passage after the shipping sack is full, heat, typically generated by ultrasonic vibrations, is applied to the exterior surface of the valve sleeve melting the thermoplastic film liner sealing the sleeve and securing the contents within the shipping sack.
However, due to the interaction between the vibrating jaw of the ultrasonic generator and the outer surface of the valve sleeve, the valve sleeve is often damaged. The damage to the valve sleeve may make it possible for the contents of the bag to leak or sift out of the bag even after the sealing operation has been completed.
Valve sleeves have been constructed of multiple sheets of paper to strengthen the valve sleeve and facilitate filling of the flexible bag. This design has a high non-conforming rate, often as great as fifteen percent, because the difficulties of aligning the several sheets of paper to the valve sleeve results in discontinuities around the valve sleeve and allow product to escape from the bag.